A physically unclonable function (PUF) may provide an unpredictable digital value. Individual PUFs may provide different digital values, even though the individual PUFs are manufactured through the same exact manufacturing process.
The PUF may be referred to as a physical one-way function (POWF) that is practically impossible to be duplicated, or a physical random function (PRF).
A characteristic of the PUF may be used to generate an encryption key for security and/or authentication. For example, a PUF may be used to provide a unique key to distinguish devices from one another.
Korean Patent Registration No. 10-1139630 (hereinafter, referred to as “'630 patent”) proposes a method of implementing a PUF. The '630 patent discloses a method of generating a PUF by probabilistically determining whether an inter-layer contact or a via is generated between conductive layers or conductive nodes of a semiconductor, based on a semiconductor process variation. In one of embodiments disclosed in the '630 patent, a via to be formed between conductive layers may be designed to have a small size and accordingly, a situation in which the via is formed, and a situation in which the via is not formed may randomly occur. In other words, a random digital value may be generated, and artificially guessing of the random digital value is impossible. However, in the '630 patent, to increase a yield of the PUF, an optimal via size needs to be determined, so that individual bit values included in a digital value generated by the PUF may correspond to a true random number, and may not be biased to either “0” or “1.”
Accordingly, a first pass of generating PUFs based on various via sizes, examining digital values generated by the PUFs, and determining an optimal via size to be used in a specific process, may be performed prior to the specific process. Additionally, a second pass of generating an actual PUF based on the determined optimal via size may be performed. However, the optimal via size may not be optimal in a predetermined wafer and/or chip, because different process variations may occur for each individual wafer and/or individual chip, even in the same process. Furthermore, despite the same process and the same line, an optimal value may be changed due to a change in a process environment or a change in various factors, over time. Accordingly, there is a desire for a method of increasing a yield of a PUF generation.